1. Field
Embodiments of the invention relate to electronic devices, and more particularly, in one or more embodiments, to radio frequency receivers.
2. Description of the Related Technology
Recently, many electronic systems have employed wireless capability. Such electronic systems can include a wireless receiver that processes a wireless signal (for example, a radio frequency signal) received via a wireless medium, such as air. A wireless receiver can include various components to amplify and/or filter a wireless signal to recover original data carried by the wireless signal.
Referring to FIG. 1, a conventional wireless radio frequency (RF) receiver system will be described below. The illustrated system 100 includes an antenna 101, an input stage structure 110, an input matching network 120, a low noise amplifier 130, a first transconductor 140a, a second transconductor 140b, a first mixer 150a, a second mixer 150b, a first local oscillator 160a, a second local oscillator 160b, a first low pass filter 170a, a second low pass filter 170b, a first analog-to-digital converter (ADC) 180a, a second analog-to-digital converter (ADC) 180b, and a digital processor 190.
The antenna 101 is configured to receive a wireless signal. The antenna 101 can be any suitable antenna for wireless signal reception. The antenna 101 provides the received wireless signal to the input stage structure 110.
The input stage structure 110 serves to receive the wireless signal from the antenna 101 and process the wireless signal. The input stage structure 110 can include, for example, an antenna interface circuit to interface with the antenna 101, and a filter (for example, a band pass filter) to filter signals outside of a signal band of interest. The input stage structure 110 provides the processed signal to the input matching network 120.
The input matching network 120 serves to improve power transfer from the input stage structure 110 to the low noise amplifier 130, and to reduce signal reflection by the low noise amplifier 130. Further, the input matching network 120 can serve to improve the noise performance of the low noise amplifier 130. The input matching network 120 is configured to match the impedance of the low noise amplifier 130 with the impedance of the structure (for example, the input stage structure 110 and the antenna 101) on the opposite side of the input matching network 120 from the low noise amplifier 130. The input matching network 120 receives the processed signal from the input stage structure 110, and provides it to the low noise amplifier 130.
The low noise amplifier 130 serves to amplify the signal from the input matching network 120, and provides the amplified signal to the first and second transconductors 140a, 140b. The low noise amplifier 130 is configured to amplify a relatively weak signal with a gain such the effect of noise on subsequent stages of the receiver system 100 is reduced.
Each of the first and second transconductors 140a, 140b serves to convert the amplified signal in voltage form into a current signal. The first and second transconductors 140a, 140b provide the current signals to the first and second mixers 150a, 150b. 
The first mixer 150a serves to mix the current signal from the first transconductor 140a and a first local frequency signal from the first local oscillator 160a to generate a first mixed signal. The first mixed signal can include the fundamental frequencies of the current signal, the first local frequency signal, harmonics thereof, and intermodulation products. The second mixer 150b serves to mix the current signal from the second transconductor 140b and a second local frequency signal from the second local oscillator 160b to generate a second mixed signal. The second mixed signal can include the fundamental frequencies of the current signal, the second local frequency signal, harmonics thereof, and intermodulation products. The mixers 150a, 150b can be biased active mixers.
In the illustrated example in which a quadrature amplitude modulation (QAM) technique is used, the first local frequency signal can be used to process in-phase (I) components of the received wireless signal while the second local frequency signal can be used to process quadrature (Q) components of the received wireless signal. The first and second local frequency signals can have a phase difference of about 90 degrees from each other.
The first and second low pass filters 170a, 170b serve to filter the first and second mixed signals, respectively, and provide the filtered signals to the first and second analog-to-digital converters 180a, 180b, respectively. The first and second low pass filters 170a, 170b can select a desired intermediate frequency (IF) and block undesired frequencies. In another embodiment, the first and second low pass filters 170a, 170b can be replaced with band pass filters.
The first and second analog-to-digital converters 180a, 180b serve to convert the filtered signals from analog form into digital signals. The first and second analog-to-digital converters 180a, 180b can provide the digital signals to the digital processor 190.
The digital processor 190 serves to receive the digital signals from the first and second analog-to-digital converters 180a, 180b, and perform digital signal processing on the digital signals. The digital signal processing can include, for example, demultiplexing and decoding.